<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    *{
      margin: 0;padding: 0;
    }
    ul{
      /* overflow: hidden; */
      float: left;
    }
    /* ul::after{
      content: '';
      display: block;
      clear: both;
    } */
    /* .clear{
      clear: both;
    } */

    li{
      list-style: none;
      width: 200px;
      height: 50px;
      background-color: aquamarine;
      float: left;
    }
    p{
      width: 100px;
      height: 100px;
      background: #000;
    }
  </style>
</head>
<body>
  <ul>
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <!-- <div class="clear"></div> -->
  </ul>

  <p>hello</p>
</body>
</html>